Re: [HACKERS] I propose killing PL/Tcl's "modules" infrastructure - Mailing list pgsql-hackers

On 02/25/2017 01:44 PM, Tom Lane wrote:
> Andrew Dunstan <andrew.dunstan@2ndquadrant.com> writes:
>> On 02/25/2017 01:14 PM, Tom Lane wrote:
>>> Now, we could try to fix this bug, and add the regression test coverage
>>> that the code clearly lacks, and upgrade the documentation about it from
>>> its currently very sad state.  But I think the right answer is just to
>>> remove the feature altogether.  It's evidently not being used, and it's
>>> kind of insecure by design, and it would not be that hard for someone
>>> to provide equivalent functionality entirely in userland if they really
>>> wanted it.
>> In PLv8 we added a parameter plv8.start_proc that names a parameterless
>> function that's executed when plv8 is first called in each session. It
>> can be used quite easily to implement something like a modules
>> infrastructure - in fact I have used it to good effect for exactly that.
>> Maybe something similar for pltcl would be a good thing.
> Yeah, the only part that's even a bit hard to replicate in userland is
> initializing the autoloading mechanism in each session.  It would be
> cleaner to provide a feature similar to what you describe that could
> be used for that purpose as well as others.  However, where does the
> "parameterless function" come from?  Is it a regular PLv8 (or for this
> purpose PL/Tcl) function expected to be present in pg_proc?
>
>             


Yes, it's a regular PLv8 function.Here's an example. It presupposes that
there is a table called plv8_modules (modname text, code text,
load_on_start boolean).
   CREATE OR REPLACE FUNCTION public.plv8_startup()    RETURNS void    LANGUAGE plv8   AS $function$     if (typeof
plv8_loaded_modules== 'undefined')       plv8_loaded_modules = {};     load_module = function(modname)     {       if
(plv8_loaded_modules[modname])          return;       var rows = plv8.execute("SELECT code from plv8_modules " +
                      " where modname = $1", [modname]);       for (var r = 0; r < rows.length; r++)       {
varcode = rows[r].code;           eval("(function() { " + code + "})")();           // plv8.elog(NOTICE,"loaded module
"+ modname);           plv8_loaded_modules[modname] = 1;       }               };     reload_module = function(modname)
   {       var rows = plv8.execute("SELECT code from plv8_modules " +                               " where modname =
$1",[modname]);       for (var r = 0; r < rows.length; r++)       {           var code = rows[r].code;
eval("(function(){ " + code + "})")();           // plv8.elog(NOTICE,"loaded module " + modname);
plv8_loaded_modules[modname]= 1;       }
 
     };
     var rows = plv8.execute("SELECT modname, code from plv8_modules   where load_on_start");     for (var r = 0; r <
rows.length;r++)     {       var modname = rows[r].modname;       if (plv8_loaded_modules[modname])           continue;
     var code = rows[r].code;       eval("(function() { " + code + "})")();       plv8_loaded_modules[modname] = 1;
 // plv8.elog(NOTICE,"loaded module " + modname);     };   $function$;
 


cheers

andrew

-- 
Andrew Dunstan                https://www.2ndQuadrant.com
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